Indium-gallium-aluminum alloys and galvanic anodes made therefrom



United States Patent 01 i'ice 3,379,636 Patented Apr. 23, 1968 ABSTRACTOF THE DISCLOSURE An aluminum alloy having a high oxidation potentialand comprising small, controlled quantities of indium and galliumalloyed with aluminum and a cast aluminum based sacrificial anodeprepared from the alloy are disclosed.

BACKGROUND OF THE INVENTION The present application is acontinuation-in-part of application Ser. No. 384,796, filed July 23,1964, and now abandoned.

This invention relates to sacrificial galvanic anodes and moreparticularly is concerned with a novel aluminum based alloy exhibitinghigh oxidation potential and a useful electrical output per unit mass ofmetal; i.e. an electrochemical equivalent which is suitable for use insuch galvanic anodes.

Theoretically, aluminum should be expected to perform satisfactorily asa galvanic anode because the element aluminum fulfills the two primaryrequirements for anodes; (1) a high theoretical oxidation potential(1.80 volts versus calomel reference) and (2) a high theoreticalelectrical output per unit mass of metal consumed (2.98 amp-hours pergram). In actual practice, however, aluminum has not proved to besatisfactory for use in such applications since it does not exhibitthese favorable theoretical properties when used as a sacrificialgalvanic anode. The presence of the normally passive oxide surface filmn the aluminum apparently presents a barrier to the oxidation of thealuminum metal thereby reducing the effective oxidation potential toabout 0.7 volt (as measured in closed circuit at either 250 or 1000milliamperes/square foot in a synthetic seawater electrolyte with astandard saturated KCl calomel cell as reference). At such low operatingvoltages, no cathodic protection is given to ferrous based structures,for example; therefore the anode exhibits no useful electrical output.By comparison, the actual working potential of magnesium is about 1.5volt and of zinc is about 1 volt.

It is known in the art to add certain elements such as gallium or indiumto aluminum in an attempt to provide an aluminum anode of commercialutility. Such additions result in some moderate increase of the workingelectropotential of aluminum.

Now, unexpectedly it has been found in the present invention thatspecific ratios and concentrations of a mixture of gallium and indiumwhen alloyed with aluminum provide a novel alloy composition exhibitingmarkedly increased electropotential over that shown by what could bepredicted from the potential exhibited by aluminumgallium oraluminum-indium binary alloys.

It is a principal object of the present invention to provide an aluminumbased galvanic anode which exhibits an unexpectedly high operatingoxidation potential and a useful ampere-hour output.

It is another object of the present invention to provide a novelaluminum alloy particularly suitable for use as a sacrificial galvanicanode.

These and other objects and advantages readily will become apparent fromthe detailed description of the invention presented hereinafter.

SUMMARY The present invention comprises a novel aluminum based alloycomposition having alloyed therewith a small amount of a mixture ofgallium and indium.

More particularly the present composition comprises aluminum havingalloyed therewith from about 0.01 to about 0.5 weight percent indium andfrom about 0.01 to about 0.2 weight percent gallium.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferably the alloy comprisesaluminum having alloyed therewith from about 0.02 to about 0.3 weightpercent indium and from about 0.02 to about 0.08 weight percent gallium.

All weight percents are based on the total composition weight.

Unexpectedly, the present novel compositions when employed assacrificial galvanic anodes exhibit a satisfactory corrosion pattern, ahigh operating oxidation potential and a satisfactory electrical outputper unit mass of metal consumed.

Galvanic anodes can be prepared from the novel compositions by use ofalloying and casting or fabricating techniques ordinarily employed inthe aluminum art. No special metal handling or fabricating operationsare required.

Aluminum for use in preparing the present novel alloy compositionsshould preferably be a relatively high purity metal (at least about99.9% Al) but can be of a lower grade metal (e.g. 99.5% Al) havingnormal production introduced impurities associated therewith. Withaluminum of 99.9% purity, gallium and indium minimum concentrations ofabout 0.02 weight percent are used for optimum oxidation potentials.With higher purity aluminum, e.g. 99.99%, potentials of greater than 1.4volts in seawater (versus saturated KCl calomel cell) are realized usingas low as 0.01 weight percent of the indium and gallium alloyingingredients. With lower purity commercial aluminum correspondinglylarger quantities of the alloying components are used to achieve thedesired high operating potentials. The alloying elements also can be ofhigh purity or of commercial grade.

The resulting alloy product is not detrimentally degraded by storage innormal atmospheres through air oxidation.

The following example will serve to further illustrate the presentinvention but is not meant to limit it thereto.

Example.A number of anodes of the present invention were prepared bymelting commercial 99.9% or 99.99% purity aluminum ingot in a graphitecrucible positioned within an electric furnace. Requisite amounts ofgallium and indium were introduced into the molten aluminum and theresulting mixture stirred to effect dispersion of the alloyingingredients throughout the melt. The resulting alloy was cast in agraphite mold into cylindrical specimens about 5 /2 inches long andabout inch in diameter. The cooling and solidification rate of thecastings were controlled such that these similated the cooling rateexperienced in production of commercial, field-sized cast anodes.

The performance of the alloys was evaluated by positioning each castcylindrical specimen (as anode) in a schedule 40 steel can 3 inches indiameter and 6 inches tall (as cathode). Synthetic seawater was used asan electrolyte with about 4 inches of each specimen being immersed. Thecells were complete with respect to electrical circuitry, a rectifierbeing employed to maintain a constant current through a group of cellsconnected in series.

The results of a number of runs comparing the performance of the novelaluminum alloy anodes of the composition of the present invention withcommercial and high purity aluminum used as a base metal for thesealloys and binary alloys of aluminum-gallium and aluminumindium anodesas controls are summarized in Table I.

TABLE I Aluminum Alloying Metal (Percent by Run (Percent weight)Potential N0. Purity) (Volts) Indium Gallium 99. 9 (Control) 0. 71 99.99(Control) 0. 72 99. 9 0. 17 (Control) 0.72 99. 99 0. 17 (Control) 1, 1399. 9 0.05 (Control) 1.07 99.99 0.21 (Control) 1.10 99. 9 0. 093 0.0131.15 99.99 0. 01 0.013 1.48 99. 9 0. 03 0. 027 1. 50 99. 9 0. 10 0. l 1.02 99. 9 0.028 0.11 1.58 99. 99 0. l2 0. 022 1. 51 99. 9 O. 23 0. 052 1.49 99. 99 0.35 0.19 1.63 99.9 0. 43 0.10 1. 63 99. 9 0. 40 0. 1. 50

-Versus standard saturated KCl calomel cell as reference and measured inclosed circuit at either 250 or 1,000 millinmpere/sqnare toot.

These results clearly show the superiority of the present novel aluminumbased gallium and indium containing ternary alloys with respect tooxidation potential as compared to aluminum, aluminum-gallium andaluminum-indium binary alloys.

These alloys exhibit a high oxidation potential which makes themsuitable for use as sacrificial anodes for applications such as galvanicpigments in paint films, galvanic anode materials for primary batteries,sacrificial galvanic coatings for sheet steel and other metals cathodicto aluminum and sacrificial anodes for cathodic protection. Additionallywhen in particulate form these compositions find utility as an activeingredient in flares, for use in chemical reductions and in thepreparation of aluminum alkyls.

Various modifications can be made in the present invention withoutdeparting from the spirit or scope thereof for it is understood that welimit ourselves only as defined in the appended claims.

We claim:

1. An aluminum alloy having a high oxidation potential, said alloycomprising;

from about 0.01 to about 0.5 weight percent indium,

from about 0.01 to about 0.2 weight percent gallium, and balancealuminum, said alloy being further characterized as containing at leastabout 0.02 weight percent each of said indium and said gallium when saidaluminum has a purity of less than about 99.99 percent aluminum.

2. An aluminum alloy having a high oxidation potential, said alloycomprising;

from about 0.02 to about 0.3 weight percent indium,

from about 0.02 to about 0.08 Weight percent gallium,

and

balance aluminum.

3. An aluminum based sacrificial galvanic anode having a minimum usefuloxidation potential of about 1.4 volts in sea water as measured versusstandard saturated KCl calomcl, which comprises;

a cast anode structure, said structure comprising;

from about 0.01 to about 0.5 weight percent indium,

from about 0.01 to about 0.2 Weight percent gallium, and balancealuminum, said alloy being further characterized as containing at leastabout 0.02 weight percent each of said indium and said gallium when saidaluminum has a purity of less than about 99.99 percent aluminum.

4. An aluminum based sacrificial galvanic anode having a minimum highuseful oxidation potential of about 1.4 volts in sea Water as measuredversus standard saturated KCl calomel, which comprises;

a cast anode structure, said structure comprising;

from about 0.02 to about 0.3 weight percent indium,

from about 0.02 to about 0.08 weight percent gallium,

and

balance aluminum.

References Cited UNITED STATES PATENTS 1,997,165 4/1935 Brown -l382,565,544- 8/1951 Brown 204l48 3,227,644 1/1966 Rutemiller 204-1973,240,688 3/1966 Pryor et al. 204l48 HOWARD S. WILLIAMS, PrimaryExaminer.

D. R. JORDAN, Assistant Examiner.

